Electrode Having Solid Electrolyte Interface And Secondary Battery Using The Same

ABSTRACT

Disclosed is an electrode having a solid electrolyte interface (SEI) film partially or totally formed on a surface thereof, the SEI film being formed by electrical reduction of a cyclic diester compound and a sulfinyl group-containing compound. Further, a secondary battery comprising the electrode is disclosed.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a divisional application of application Ser.No. 12/310,489 filed on Aug. 24, 2007, based on a national phase entryunder 35 U.S.C. §371 of International Application No. PCT/KR2007/004054,filed Aug. 24, 2007, published in English, which claims the benefit ofKorean Patent Application No. 10-2006-0081297, filed Aug. 25, 2006. Thedisclosures of said applications are incorporated by reference herein.

BACKGROUND OF THE INVENTION

Recently, there is an increasing interest in energy storage technology.Batteries have been widely used as energy sources in portable phones,camcorders, notebook computers, PCs and electric cars, resulting inintensive research and development into them. In this regard,electrochemical devices are subjects of great interest. Particularly,development of rechargeable secondary batteries is the focus ofattention.

Among secondary batteries which are now in use, lithium secondarybatteries developed in the early 1990s are in the spotlight due to theadvantages of higher drive voltages and far greater energy densitiesthan those of conventional batteries using an aqueous electrolyte, suchas Ni-MH, Ni—Cd and H₂SO₄—Pb batteries.

A secondary battery includes a cathode, an anode, a separator, and anelectrolyte comprising an electrolyte solvent and an electrolyte salt.Meanwhile, a conventional secondary battery comprising an anode formedof a carbonaceous material and a cathode formed of a lithium metal oxidehas an average discharge voltage of 3.6˜3.7V. To obtain such a drivevoltage, it is necessary to provide an electrolyte composition that isstable in a charge/discharge voltage range of the battery, for example,in a range of 0 to 4.2V.

However, currently used electrolyte solvents have problems in that theyare decomposed on the surface of an electrode during charge/dischargecycles of a battery, and are co-intercalated into a gap betweencarbonaceous anode active material layers to cause a structural collapseof the anode, resulting in degradation of the stability of the battery.Meanwhile, it has been known that the above problems could be solved bya solid electrolyte interface (SEI) film formed on the surface of ananode via the reduction of the electrolyte solvent upon the first chargecycle of the battery. However, the SEI film is not sufficient to serveas a lasting protective film for the anode. Therefore, the aboveproblems still remain unsolved during repeated charge/discharge cycles,and may cause a drop in lifespan characteristics of the battery.Particularly, the SEI film is not thermally stable, and thus may beeasily broken down by electrochemical energy and heat energy increasingwith the lapse of time when the battery is driven or stored at hightemperature. Accordingly, gases including CO₂ are generated continuouslydue to the collapse of the SEI film, decomposition of the electrolyte,etc., under such high temperature conditions, resulting in an increasein the internal pressure and thickness of the battery.

To solve the aforementioned problems, a method using vinylene carbonate(referred to also as VC hereinafter) as an electrolyte additive capableof forming a SEI film on an anode is suggested. However, the SEI filmformed by VC is decomposed with ease when exposed under high temperatureconditions, resulting in degradation of the high temperature stabilityof a battery.

SUMMARY OF THE INVENTION

Therefore, the present invention has been made in view of theabove-mentioned problems. It is an aspect of the present invention toprovide an electrolyte comprising both a cyclic diester compound and asulfinyl group-containing compound in order to optimize the physical andthermal stability of an SEI film formed on the surface of an anode, toimprove lifespan characteristics of a battery, and to ensurehigh-temperature stability of a battery.

The present invention provides an electrolyte comprising an electrolytesalt and an electrolyte solvent, the electrolyte further comprising botha cyclic diester compound and a sulfinyl group-containing compound. Thepresent invention also provides a secondary battery comprising the sameelectrolyte.

Further, the present invention provides an electrode having a solidelectrolyte interface (SEI) film partially or totally formed on asurface thereof, the SEI film being formed by electrical reduction of acyclic diester compound and a sulfinyl group-containing compound. Thepresent invention also provides a secondary battery comprising the sameelectrode.

Hereinafter, the present invention will be explained in more detail.

As described above, the SEI film formed on the surface of an anode by aconventional electrolyte composition is a physically weak film, and thusis easily broken down due to lithium intercalation/deintercalationduring charge/discharge cycles of a battery. Also, the SEI film has lowthermal stability, and thus may be thermally decomposed with ease, whenthe battery is stored or operated at high temperature, to causegeneration of CO₂ or the like. As a result, the battery shows a swellingphenomenon including an increase in its thickness due to continuous gasgeneration under high temperature. This may lead to serious problems invarious products using the battery, including mobile phones, notebookcomputers, etc.

There have been many attempts to add various electrolyte additivescapable of forming SEI films to an electrolyte so as to improvestability of the SEI films. However, according to the prior art, it isnot possible to improve the thermal stability and physical property ofthe SEI film at the same time.

Under these circumstances, according to the present invention, compoundshaving different thermal and physical stability characteristics,particularly a cyclic diester compound and a sulfinyl group-containingcompound showing different densities in the resultant SEI films, areused in combination as electrolyte additives. By doing so, the presentinvention makes it possible to optimize physical stability and thermalstability of the SEI film formed on the surface of an anode. Suchoptimization of the battery quality may be explained as follows, but isnot limited thereto.

The SEI film formed by a cyclic diester compound is firm but has lowthermal stability, while the SEI film formed by a sulfinylgroup-containing compound has excellent thermal stability but is aphysically weak film.

Additionally, the cyclic diester compound forms a relatively dense SEIfilm, while the sulfinyl group-containing compound forms a relativelyporous SEI film. Due to such different densities, when the abovecompounds are used in combination as additives for an electrolyteaccording to the present invention, an SEI film is formed by onecomponent, and then an additional SEI film may be formed by the othercomponent on a thin or porous portion of the first SEI film or on aportion of the surface of an anode having no SEI film. As a result, theSEI films, each formed by the above compounds, cooperate with each otherto provide an SEI film having excellent thermal stability and physicalstability at the same time. Particularly, the SEI film according to thepresent invention includes two different kinds of SEI films stackedsuccessively, and thus can show excellent rigidity. Therefore, it ispossible to minimize a drop in the capacity of a battery during repeatedcharge/discharge cycles, and to improve both lifespan characteristicsand high-temperature stability of a battery at the same time.

The non-aqueous electrolyte according to the present invention comprisesboth a cyclic diester compound and a sulfinyl group-containing compound.

Herein, the cyclic diester compound and the sulfinyl group-containingcompound preferably have the difference tolerance of 0 to 0.5V (morepreferably 0˜0.3V) in reduction potentials vs. Li+/Li. If the differencetolerance in reduction potentials vs. Li+/Li is too high, an SEI film isformed predominantly by any one component. Thus, it may be difficult toadequately control thermal stability and physical stability of the SEIfilm.

There is no particular limitation in the cyclic diester compound, aslong as the compound contains two ester groups in its ring backbone. Thecyclic diester compound may include a compound represented by thefollowing Formula 1, and non-limiting examples thereof includeglycolide, methyl glycolide, lactide, tetramethyl glycolide,fluoroglycolide, vinylglycolide, or the like.

wherein each of R₁˜R₄ independently represents a hydrogen atom, halogenatom, C1˜C10 alkyl group, C2˜C10 alkenyl group, or a halogen-substitutedalkyl or alkenyl group.

Additionally, the sulfinyl (S═O) group-containing compound may includesulfone, sulfite, sulfonate and sultone (cyclic sulfonate), and theabove compounds may be used alone or in combination. Herein, the sulfonecompound may be represented by the following Formula 2 and includesdivinyl sultone. The sulfite compound may be represented by thefollowing Formula 3, and includes ethylene sulfite or propylene sulfite.The sulfonate compound may be represented by the following Formula 4 andincludes diallyl sulfonate. Further, non-limiting examples of thesultone compound include propane sultone, butane sultone, propenesultone, or the like.

wherein each of R₁ and R₂ independently represents a hydrogen atom,halogen atom, C1˜C10 alkyl group, C2˜C10 alkenyl group, or ahalogen-substituted alkyl or alkenyl group.

The cyclic diester compound and the sulfinyl group-containing compoundmay be used in a controlled amount as desired to improve the quality ofa battery. Preferably, the cyclic diester compound is used in an amountof 0.1˜10 parts by weight per 100 parts by weight of the electrolyte. Ifthe cyclic diester compound is used in an amount of less than 0.1 partsby weight, it is not possible to improve lifespan characteristics of abattery sufficiently. If the cyclic diester compound is used in anamount of greater than 10 parts by weight, the amount of irreversiblelithium required for forming the SEI film increases, resulting in asignificant loss in the capacity of a battery. Additionally, thesulfinyl group-containing compound is used preferably in an amount of0.5 5 parts by weight per 100 parts by weight of the electrolyte. If thesulfinyl group-containing compound is used in an amount of less than 0.5parts by weight, it is not possible to improve high-temperaturestability characteristics of a battery sufficiently. If the sulfinylgroup-containing compound is used in an amount of greater than 5 partsby weight, the amount of irreversible lithium required for forming theSEI film increases, resulting in a significant loss in the capacity of abattery.

The electrolyte for a battery, to which the cyclic diester compound andthe sulfinyl group-containing compound is added according to the presentinvention, further may comprise conventional components widely known toone skilled in the art, for example, an electrolyte salt and anelectrolyte solvent.

The electrolyte salt that may be used in the present invention includesa salt represented by the formula of A⁺B⁻, wherein A⁺ represents analkali metal cation selected from the group consisting of Li⁺, Na⁺, K⁺and combinations thereof, and B⁻ represents an anion selected from thegroup consisting of PF₆ ⁻, BF₄ ⁻, Cl⁻, Br⁻, I⁻, ClO₄ ⁻, AsF₆, CH₃CO₃ ⁻,N(CF₃SO₂)₂ ⁻, C(CF₂SO₂)₃ ⁻ and combinations thereof. A lithium salt isparticularly preferred.

The electrolyte solvent that may be used in the present inventionincludes cyclic carbonates, linear carbonates, lactone, ether, ester,acetonitrile, lactam, ketone, or the like. Non-limiting examples of thecyclic carbonates include ethylene carbonate (EC), propylene carbonate(PC), butylene carbonate (BC), fluoroethylene carbonate (FEC), or thelike. Non-limiting examples of the linear carbonates include diethylcarbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC),ethyl methyl carbonate (EMC), methyl propyl carbonate (MPC), or thelike. Non-limiting examples of the lactone include gamma-butyrolactone(GBL), and Non-limiting examples of the ether include dibutyl ether,tetra hydro furan, 2-methyl tetra hydro furan, 1,4-dioxane, diethoxyethane dimethoxy ethane, or the like. Non-limiting examples of the esterinclude methyl formate, ethyl formate, propyl formate, methyl acetate,ethyl acetate, propyl acetate, pentyl acetate, methyl propionate, ethylpropionate, propyl propionate, butyl propionate, methyl pivalate, or thelike. Non-limiting examples of the ketone include poly methyl vinylketone. Halogen derivatives of the above electrolyte solvents may alsobe used. The above electrolyte solvents may used alone or incombination.

Additionally, the present invention provides an electrode (preferably ananode) having a solid electrolyte interface (SEI) film partially ortotally formed on a surface thereof, the SEI film being formed byelectrical reduction of a cyclic diester compound and a sulfinylgroup-containing compound. The electrode can be obtained by subjectingto at least one charge/discharge cycle after assembling a unit cellusing an electrode manufactured by a conventional method known to oneskilled in the art and an electrolyte comprising the cyclic diestercompound and the sulfinyl group-containing compound, so that a SEI filmcan be formed on the surface of the electrode active material. In avariant, before assembling a unit cell, an electrode manufactured by aconventional method known to one skilled in the art is subjected toelectrical reduction while the electrode is dipped into an electrolytecomprising the cyclic diester compound and the sulfinyl group-containingcompound, so as to obtain an electrode having a preliminarily formed SEIfilm thereon.

The electrode having no SEI film can be obtained by a conventionalmethod known to one skilled in the art. In one embodiment of suchconventional methods, electrode slurry is prepared by mixing andagitating an electrode active material and a solvent optionally with abinder, a conductive agent and a dispersant, and then the slurry isapplied (coated) onto a metallic current collector, followed bycompressing and drying.

Anode active materials may include any conventional anode activematerials currently used in an anode of a conventional secondarybattery. Particular non-limiting examples of the anode active materialinclude lithium intercalation materials such as lithium metal, lithiumalloys, carbon, petroleum coke, activated carbon, graphite or othercarbonaceous materials. Non-limiting examples of an anode currentcollector include foil formed of copper, gold, nickel, copper alloys ora combination thereof.

Further, the secondary battery according to the present inventionincludes an electrolyte comprising both a cyclic diester compound and asulfinyl group-containing compound, and/or an electrode having a solidelectrolyte interface (SEI) film partially or totally formed on asurface thereof, the SEI film being formed by electrical reduction of acyclic diester compound and a sulfinyl group-containing compound.

Preferably, the present invention provides a secondary batterycomprising: a separator; a cathode; an anode having a SEI film partiallyor totally formed on a surface thereof, the SEI film being formed byelectrical reduction of a cyclic diester compound and a sulfinylgroup-containing compound; and/or an electrolyte comprising both acyclic diester compound and a sulfinyl group-containing compound.

Preferably, the secondary battery is a lithium secondary battery, andnon-limiting examples of the lithium secondary battery include a lithiummetal secondary battery, a lithium ion secondary battery, a lithiumpolymer secondary battery or a lithium ion polymer secondary battery.

Particularly, cathode active materials may include any conventionalcathode active materials currently used in a cathode of a conventionalsecondary battery. Particular non-limiting examples of the cathodeactive material include: lithium transition metal composite oxides,including LiM_(x)O_(y) (wherein M=Co, Ni, Mn, CO_(a)Ni_(b)Mn_(c)), suchas lithium manganese composite oxides (e.g. LiMn₂O₄), lithium nickeloxides (e.g. LiNiO₂), lithium cobalt oxides (e.g. LiCoO₂), or otheroxides containing other transition metals partially substituting formanganese, nickel and cobalt; chalcogenide (e.g. manganese dioxide,titanium disulfide, molybdenum disulfide, etc.); or the like. Amongthese examples, LiCoO₂, LiNiO₂, LiMnO₂, LiMn₂O₄,Li(Ni_(a)CO_(b)Mn_(c))O₂ (wherein 0<a<1, 0<b<1, 0<c<1, a+b+c=1),LiNi_(1-Y)Co_(Y)O₂, LiCO_(1-Y)Mn_(Y)O₂, LiNi_(1-Y)Mn_(Y)O₂ (wherein0≦Y<1), Li(Ni_(a)CO_(b)Mn_(c))O₄ (0<a<2, 0<b<2, 0<c<2, a+b+c=2),LiMn_(2-z)Ni_(z)O₄, LiMn_(2-z)Co_(z)O₄ (wherein 0<Z<2), LiCoPO₄, LiFePO₄or a mixture thereof is particularly preferred. Non-limiting examples ofa cathode current collector include foil formed of aluminum, nickel or acombination thereof.

Preferably, the separator is a porous separator. Non-limiting examplesof the separator that may be used include a polypropylene-based,polyethylene-based or polyolefin-based separator.

The secondary battery according to the present invention may be obtainedby using a method generally known to one skilled in the art. Forexample, an electrode assembly is formed by using a cathode, an anodeand a separator interposed between both electrodes, and then theabove-described electrolyte is injected thereto.

There is no particular limitation in the outer shape of the secondarybattery obtained in the above-described manner. The secondary batterymay be a cylindrical, prismatic, pouch-type or coin-type battery.

DETAILED DESCRIPTION

Reference will now be made in detail to the preferred embodiments of thepresent invention. It is to be understood that the following examplesare illustrative only and the present invention is not limited thereto.

Example 1

To 100 parts by weight of a solution containing 1M LiPF₆ in ethylenecarbonate (EC) and diethyl carbonate (DEC) mixed in a weight ratio of1:1, 2.0 parts by weight of glycolide (Formula 5) and 3.0 parts byweight of propane sultone were added to provide an electrolyte.

Example 2

An electrolyte was provided in the same manner as described in Example1, except that ethylene sulfite was used instead of propane sultone.

Example 3

An electrolyte was provided in the same manner as described in Example1, except that lactide (Formula 6) was used instead of glycolide.

Comparative Example 1

An electrolyte was provided in the same manner as described in Example1, except that glycolide was used alone.

Comparative Example 2

An electrolyte was provided in the same manner as described in Example1, except that 2.0 parts by weight of lactide was used alone instead ofglycolide and propane sultone.

Comparative Example 3

An electrolyte was provided in the same manner as described in Example1, except that propane sultone was used alone.

Comparative Example 4

An electrolyte was provided in the same manner as described in Example1, except that 3.0 parts by weight of ethylene sulfite was used aloneinstead of glycolide and propane sultone.

Comparative Example 5

An electrolyte was provided in the same manner as described in Example1, except that no additive was added to the electrolyte.

Experimental Example 1 Measurement of Reduction Voltages of ElectrolyteAdditives

The following experiment was performed to measure reduction potentialsof the cyclic diester compound and sulfinyl group-containing compoundused in the present invention.

The electrolytes according to Comparative Examples 1˜5 were used alongwith artificial graphite as a cathode and lithium foil as an anode toprovide coin type half cells in the conventional manner. The coin typehalf cells were subjected to cyclic voltammetry in a range of 1.5V˜1 mVat a scanning rate of 0.1 mV/sec in order to measure the peak reductionvoltages. The results are shown in the following Table 1. For reference,it is to be noted that experimental results of reduction voltagesobtained by using full cells under the same conditions are contrary tothe following results.

TABLE 1 Peak reduction voltage Electrolyte Additive (V vs Li) Comp. Ex.1 Glycolide 2 wt % 1.1 Comp. Ex. 2 Lactide 2 wt % 0.9 Comp. Ex. 3Propane sultone 3 wt % 1 Comp. Ex. 4 Ethylene sulfite 3 wt % 1.2 Comp.Ex. 5 None 0.6

After the experiment for the half cells, the electrolytes containing thecyclic diester compound or sulfinyl group-containing compound addedthereto according to Comparative Examples 1˜4 showed different reductionvoltages as compared to the electrolyte containing no additive. Thissuggests that each of the voltages measured in Comparative Examples 1˜4means the reduction potential of each additive.

Particularly, the cyclic diester compound and the sulfinylgroup-containing compound show higher reduction voltages as compared tothe conventional electrolyte (Comparative Example 5). It can beestimated from the above results that the above compounds are reduced inadvance of the electrolyte in a secondary battery, which is a full cell,to form an SEI film on the surface of an anode.

Experimental Example 2 Evaluation of Lifespan Characteristics of LithiumSecondary Batteries

The electrolytes according to Examples 1˜3 and Comparative Examples 1˜5were used along with LiCoO₂ as a cathode and artificial graphite as ananode to provide coin type cells in the conventional manner. The cointype cells were subjected to 200 charge/discharge cycles at 0.5 C andthe capacity maintenance of each cell was measured based on the initialcapacity. The results are shown in the following Table 2.

Experimental Example 3 Evaluation of High-Temperature Stability ofLithium Secondary Batteries

The electrolytes according to Examples 1˜3 and Comparative Examples 1˜5,LiCoO₂ as a cathode and artificial graphite as an anode were used toprovide aluminum pouch type bicells in the conventional manner. Thecells were fully charged, stored at 90° C. for 6 hours, and then theincrement in the thickness of each cell was measured. The results areshown in the following Table 2.

TABLE 2 Capacity Thickness Maintenance increment Electrolyte Additive(%) (mm) Ex. 1 Glycolide 2 wt % 82.1 0.2 Propane sultone 3 wt % Ex. 2Glycolide 2 wt % 80.3 0.3 Ethylene sulfite 3 wt % Ex. 3 Lactide 2 wt %80.5 0.1 Propane sultone 3 wt % Comp. Ex. 1 Glycolide 2 wt % 62.1 1.2Comp. Ex. 2 Lactide 2 wt % 57.5 1.1 Comp. Ex. 3 Propane sultone 3 wt %49.3 0.4 Comp. Ex. 4 Ethylene sulfite 3 wt % 52.6 0.3 Comp. Ex. 5 None43.3 1.4

After the experiment, the cells using the cyclic diester compound or thesulfinyl group-containing compound alone according to ComparativeExamples 1˜4 showed a slight increase (merely about 50˜60%) in thedischarge capacity maintenance as compared to the cell using noelectrolyte additive according to Comparative Example 5. However, thecells using the cyclic diester compound in combination with the sulfinylgroup-containing compound as electrolyte additives according to Examples1˜3 showed a capacity maintenance of 80% or higher. This demonstratesthat the combination of a cyclic diester compound with a sulfinylgroup-containing compound as electrolyte additives can significantlyimprove lifespan characteristics of a battery as compared to a batteryusing each compound alone.

Additionally, it could be seen from the experimental results that thecells of Examples 1˜3 according to the present invention showed asignificant drop in the thickness increment under high-temperatureconditions as compared to the cell according to Comparative Example 5.This demonstrates that the combination of a cyclic diester compound witha sulfinyl group-containing compound as electrolyte additives cansignificantly improve lifespan characteristics of a battery and canensure excellent high-temperature stability of a battery at the sametime.

Experimental Example 4 Investigation of SEI Film Formation on Anode ViaReaction of Additive

The electrolytes according to Examples 1˜3 and Comparative Examples 1˜5were used along with artificial graphite as a cathode and lithium foilas an anode were used to provide a coin type half cell in theconventional manner. Each of the coin type half cells was subjected tothree times of charge/discharge cycles under 0.2 C at 23° C., each cellwas disassembled in a discharged state, and then the anode was collectedfrom each cell.

The anode was analyzed by DSC (differential scanning calorimetry) andthe initial heat emission temperature was measured. The results areshown the following Table 3. It is generally thought that the initialheat emission is the result of the thermal degradation of the SEI filmon the surface of the anode. Also, a higher initial heat emissiontemperature indicates that the SEI film formed on the surface of theanode has higher thermal stability.

TABLE 3 Initial heat emission Electrolyte additive temperature (° C.)Ex. 1 Glycolide 2 wt % 125 Propane sultone 3 wt % Ex. 2 Glycolide 2 wt %120 Ethylene sulfite 3 wt % Ex. 3 Lactide 2 wt % 128 Propane sultone 3wt % Comp. Ex. 1 Glycolide 2 wt % 103 Comp. Ex. 2 Lactide 2 wt % 112Comp. Ex. 3 Propane sultone 3 wt % 123 Comp. Ex. 4 Ethylene sulfite 3 wt% 119 Comp. Ex. 5 None 107

After the experiment, the cells using a cyclic diester compound incombination with a sulfinyl group-containing compound as electrolyteadditives according to Examples 1˜3 and the cells using each of theabove compounds alone according to Comparative Examples 1˜5 showeddifferent initial heat emission temperatures at the anodes. It can beseen from the above experimental results that the compounds used in theelectrolyte according to the present invention, i.e. both the cyclicdiester compound and the sulfinyl group-containing compound participatein the formation of the SEI films.

For reference, the cells of Examples 1˜3 according to the presentinvention showed a initial heat emission temperature of 120° C. orhigher. This demonstrates that the combination of the cyclic diestercompound with the sulfinyl group-containing compound allows formation ofan SEI film having excellent thermal stability.

INDUSTRIAL APPLICABILITY

As can be seen from the foregoing, the electrolyte according to thepresent invention can optimize thermal stability and physical stabilityof an SEI film formed on the surface of an anode, can improve lifespancharacteristics of a battery, and can ensure high-temperature stabilityof a battery.

Although several preferred embodiments of the present invention havebeen described for illustrative purposes, those skilled in the art willappreciate that various modifications, additions and substitutions arepossible, without departing from the scope and spirit of the inventionas disclosed in the accompanying claims.

1. An electrode having a solid electrolyte interface (SEI) filmpartially or totally formed on a surface thereof, the SEI film beingformed by electrical reduction of a cyclic diester compound and asulfinyl group-containing compound, wherein the cyclic diester compoundis not lactide.
 2. The electrode as claimed in claim 1, wherein thecyclic diester compound is selected from the group consisting ofglycolide, methyl glycolide, tetramethyl glycolide, fluoroglycolide andvinyl glycolide.
 3. The electrode as claimed in claim 1, wherein thesulfinyl group-containing compound is selected from the group consistingof sulfone, sulfite, sulfonate and sultone.
 4. The electrode as claimedin claim 1, wherein the sulfinyl group-containing compound is selectedfrom the group consisting of divinyl sulfone, ethylene sulfite,propylene sulfite, diallyl sulfonate, propane sultone, butane sultoneand propene sultone.
 5. A secondary battery comprising a cathode, ananode and an electrolyte, wherein the electrolyte comprises anelectrolyte salt and an electrolyte solvent, the electrolyte furthercomprising both a cyclic diester compound and a sulfinylgroup-containing compound; and/or the cathode or the anode is theelectrode having a solid electrolyte interface (SEI) film partially ortotally formed on a surface thereof, the SEI film being formed byelectrical reduction of a cyclic diester compound and a sulfinylgroup-containing compound, wherein the cyclic diester compound is notlactide.
 6. The secondary battery as claimed in claim 5, wherein thecyclic diester compound and the sulfinyl group-containing compound havethe difference tolerance of 0 to 0.5V in reduction potentials vs.Li+/Li.
 7. The secondary battery as claimed in claim 5, wherein thecyclic diester compound and the sulfinyl group-containing compound havethe difference tolerance of 0 to 0.3V in reduction potentials vs.Li+/Li.
 8. The secondary battery as claimed in claim 5, wherein thecyclic diester compound is represented by the following Formula 1:

wherein each of R₁˜R₄ independently represents a hydrogen atom, halogenatom, C1˜C10 alkyl group, C2˜C10 alkenyl group, or a halogen-substitutedalkyl or alkenyl group, wherein the cyclic diester compound is notlactide.
 9. The secondary battery as claimed in claim 5, wherein thecyclic diester compound is selected from the group consisting ofglycolide, methyl glycolide, tetramethyl glycolide, fluoroglycolide andvinyl glycolide.
 10. The secondary battery as claimed in claim 5,wherein the sulfinyl group-containing compound is selected from thegroup consisting of sultone, sulfite, sulfonate and sultone.
 11. Thesecondary battery as claimed in claim 5, wherein the sulfinylgroup-containing compound is selected from the group consisting of thecompounds represented by the following Formula 2, Formula 3 and Formula4:

wherein each of R₁ and R₂ independently represents a hydrogen atom,halogen atom, C1˜C10 alkyl group, C2˜C10 alkenyl group, or ahalogen-substituted alkyl or alkenyl group.